Iron-Nickel-Chrome-Silicon-Alloy

ABSTRACT

Iron-nickel-chromium-silicon alloy having (in % by weight) 34 to 42% nickel, 18 to 26% chromium, 1.0 to 2.5% silicon, and additives of 0.05 to 1% Al, 0.01 to 1% Mn, 0.01 to 0.26% lanthanum, 0.0005 to 0.05% magnesium, 0.01 to 0.14% carbon, 0.01 to 0.14% nitrogen, max. 0.01% sulfur, max. 0.005% B, remainder iron and the usual impurities resulting from the production process.

The invention relates to an iron-nickel-chromium-silicon alloy havingimproved service life and dimensional stability.

Austenitic iron-nickel-chromium-silicon alloys having different nickel,chromium, and silicon contents have been used for some time as heatconductors in temperatures ranging up to 1100° C. This alloy group isstandardized in DIN 17470 (Table 1) and ASTM B344-83 (Table 2). Table 3lists a number of commercially available alloys for this standard.

The sharp increase in the price of nickel in recent years has given riseto the desire to use heat conductor alloys that have the lowest possiblenickel content. In particular there is a desire to replace the highnickel-content variants NiCr8020, NiCr7030, and NiCr6015 (Table 1),which are distinguished by particularly advantageous properties, withmaterials having a reduced nickel content without having to make majorsacrifices in the performance of the material.

In general it should be noted that the service life and the usagetemperature of the alloys listed in Tables 1 and 2 increase as nickelcontent increases. All of these alloys form a chromium oxide layer(Cr₂O₃) with a more or less closed SiO₂ layer disposed thereunder. Smalladditions of elements with high affinity for oxygen, such as Ce, Zr, Th,Ca, Ta (Pfeifer/Thomas, Zunderfeste Legierungen [Non-scaling Alloys],2nd edition, Springer Verlag 1963, pages 258 and 259) increase theservice life, in the aforesaid case only the effect of a single elementwith affinity for oxygen having been investigated, but no informationhaving been provided on the effect of combining such elements. As a heatconductor is used, the chromium content is slowly consumed for buildingthe protective layer. Therefore the service life is increased by ahigher chromium content because a higher content of the elementchromium, which forms the protective layer, delays the point in time atwhich the Cr content is below the critical limit and oxides other thanCr₂O₃ form, which are e.g. iron-containing oxides.

Known from EP-A 0 531 775 is a heat-resistant thermally moldableaustenitic nickel alloy having the following composition (in % byweight):

C 0.05-0.15% Si 2.5-3.0% Mn 0.2-0.5% P max. 0.015% S max. 0.005% Cr25-30% Fe 20-27% A10.05-0.15% Cr 0.001-0.005% SE 0.05-0.15% N 0.05-0.20%

remainder Ni and impurities related to the melting process.

EP-A 0 386 730 describes a nickel-chromium-iron alloy that has very goodoxidation resistance and heat resistance as is desired for advanced heatconductor applications and that proceeds from the known heat conductoralloy NiCr6015 and in which it was possible to attain significantimprovements in usage properties by adjusting to one anothermodifications made to the composition. The alloy is distinguished fromthe known NiCr6015 material in particular in that the rare earth metalsare replaced with yttrium, in that they also contain zirconium andtitanium, and in that the nitrogen content is adjusted in a specialmanner to the zirconium and titanium content.

From WO-A 2005/031018 can be taken an austenitic Fe—Cr—Ni alloy for usein the high temperature range that has largely the following chemicalcomposition (in % by weight):

Ni 38-48% Cr 18-24% Si 1.0-1.9% C<0.1%

Fe remainder

For free-hanging heating elements, in addition to the requirement for along service life there is also the requirement for good dimensionalstability at the application temperature. A coil that sags too muchduring operation (sagging) results in uneven spacing of the windings anduneven temperature distribution, shortening service life. In order tocounteract this, more support points would be necessary for the heatingcoil, which increases the costs. This means that the heat conductormaterial must have sufficiently good dimensional stability and creepresistance.

The creep mechanisms that have a negative impact on dimensionalstability in the application temperature range (dislocation creep, grainboundary migration, and diffusion creep) are all influenced towardgreater creep resistance by a large grain size (except for dislocationcreep). Dislocation creep is not a function of grain size. Producing awire with a large grain size increases creep resistance and thereforedimensional stability. Grain size should therefore also be considered asan important factor.

Also significant for a heat conductor material is the highest possiblespecific electrical resistance and the lowest possible change in theheat resistance/cold resistance ratio with the temperature (temperaturecoefficient ct).

In particular the variants with lower nickel content, NiCr3020 and 35Ni,20Cr (Table 1 and Table 2), which are distinguished by significantlylower costs, do not satisfactorily fulfill the service liferequirements.

The object is thus to design an alloy that, with significantly lowernickel content than NiCr6015 and thus with significantly lower costs,has

-   a) high oxidation resistance and thus concomitant long service life;-   b) sufficiently good dimensional stability at the application    temperature;-   c) high specific electrical resistance in conjunction with the least    possible change in the heat resistance/cold resistance ratio with    the temperature (temperature coefficient ct).

This object is attained using an iron-nickel-chromium-silicon alloyhaving (in % by weight) 34 to 42% nickel, 18 to 26% chromium, 1.0 to2.5% silicon, and additives of 0.05 to 1% Al, 0.01 to 1% Mn, 0.01 to0.26% lanthanum, 0.0005 to 0.05% magnesium, 0.01 to 0.14% carbon, 0.01to 0.14% nitrogen, max. 0.01% sulfur, max. 0.005% B, remainder iron andthe usual impurities resulting from the production process.

Advantageous refinements of the inventive subject-matter can be found inthe associated subordinate claims.

Due to its special composition, this alloy has a longer service lifethan the alloys according to the prior art that have the same nickel andchromium content. In addition, with 0.04 to 0.10% carbon it is possibleto attain increased dimensional stability and less sagging than with thealloys according to the prior art.

The range for the element nickel is between 34 and 42%, wherein,depending on employment, the nickel content can be as follows:

-   -   34-39%    -   34-38%    -   34-37%    -   37-38%.

The chromium content is between 18 and 26%, wherein depending on thearea of employment, here as well, the chromium content can be asfollows:

-   -   20-24%    -   21-24%

The silicon content is between 1.0 and 2.5%, wherein, depending on thearea of application, the defined content can be adjusted within therange:

-   -   1.5-2.5%    -   1.0-1.5%    -   1.5-2.0%    -   1.7-2.5%    -   1.2-1.7%    -   1.7-2.2%    -   2.0-2.5%

The element aluminum is provided as an additive, specifically aluminumcontent is 0.05 to 1%. It can preferably also be adjusted as follows inthe alloy:

-   -   0.1-0.7%

The same applies for the element manganese, which is added at 0.01 to 1%of the alloy. The following range is also alternatively conceivable:

-   -   0.1-0.7%

The inventive subject-matter preferably proceeds from the fact that thematerial properties provided in the examples are largely adjusted byadding the element lanthanum for a lanthanum content of 0.01 to 0.26%.Depending on the area of application, defined values can be adjusted inthe alloy here as well:

-   -   0.01-0.2%    -   0.02-0.15%    -   0.04-0.15%

This also applies analogously for the element nitrogen, which is addedto attain nitrogen content between 0.01 and 0.14%. Defined content canbe provided as follows:

-   -   0.02-0.10%    -   0.03-0.09%

Carbon is added to the alloy analogously, specifically to attain carboncontent between 0.01 and 0.14%. Content can be adjusted specifically asfollows in the alloy:

-   -   0.04-0.14%    -   0.04-0.10%

Magnesium is also among the elements that can be added to attainmagnesium content of 0.0005 to 0.05%. Specifically it is possible toadjust this element as follows in the alloy:

-   -   0.001-0.05%    -   0.008-0.05%

The elements sulfur and boron can be present in the alloy as follows:

Sulfur max. 0.005% Boron max. 0.003%

Moreover, the calcium content of the alloy can be between 0.005 and0.07%, in particular 0.001 to 0.05% or 0.01 to 0.05%.

If the effectiveness of the reactive element lanthanum alone is notadequate for producing the material properties set forth in thestatement of the object, the alloy can moreover contain at least one ofthe elements Ce, Y, Zr, Hf, Ti at a content of 0.01 to 0.3%, which canalso be defined additives as needed.

Additions of elements with an affinity for oxygen, such as La, Ce, Y,Zr, Hf, and Ti improve service life. They do this in that they areincluded in the oxide layer and there block the diffusion path of theoxygen on the grain boundaries. The quantity of the element availablefor this mechanism must therefore be calibrated to the atomic weight inorder to be able to compare the quantities of different elements to oneanother.

The potential of the effective elements (PwE) is therefore defined as

PwE=200·Σ(X _(E)/atomic weight of E)

where E is the element in question and X_(E) is the content of theelement in question in percent.

As already addressed, the alloy can contain 0.01 to 0.3% of one or moreof the elements La, Ce, Y, Zr, Hf, Ti, wherein

ΣPwE=1.43·X_(Ce)+1.49*X_(La)+2.25·X_(Y)+2.19·X_(Zr)+1.12X_(Hf)+4.18·X_(Ti)≦0.38,in particular ≦0.36 (at 0.01 to 0.2% of the entire element), wherein PwEequals the potential of the effective elements.

Alternatively, when at least one of the elements La, Ce, Y, Zr, Hf, Tiis present in contents of 0.02 to 0.10%, it is possible for the sumPwE=1.43·X_(Ce)+1.49·X_(La)+2.25·X_(Y)+2.19·X_(Zr)+1.12·X_(Hf)+4.18·X_(Ti)to be less than or equal to 0.36, wherein PwE equals the potential ofthe effective elements.

The alloy can moreover have a phosphorous content between 0.01 to 0.20%,in particular 0.005 to 0.020%.

Moreover, the alloy can contain between 0.01 and 1.0% of one or more ofthe elements Mo, W, V, Nb, Ta, Co, which can furthermore be limited asfollows:

-   -   0.01 to 0.2%    -   0.01 to 0.06%

Finally, the elements copper, lead, zinc, and tin can be present asimpurities in contents as follows:

Cu max. 1.0% Pb max. 0.002% Zn max. 0.002% Sn max. 0.002%

The inventive alloy is to be used in electrical heating elements, inparticular electrical heating elements that require high dimensionalstability and not much sagging.

One specific application for the inventive alloy is its use inconstructing furnaces.

The inventive subject-matter is described in greater detail using thefollowing examples.

EXAMPLES

As stated in the foregoing, Tables 1 through 3 reflect the prior art.

Tables 4a and 4b depict industrial-scale meltediron-nickel-chromium-silicon alloys according to the prior art T1through T7, an alloy melted on the laboratory scale according to theprior art T8, and a plurality of inventive test alloys V771 throughV777, V1070 through V1076, V1090 through V1093, melted on the laboratoryscale, for optimizing the alloy composition.

For the alloys T8 melted on the laboratory scale, V771-V777,V1070-V1076, V1090-V1093, a soft annealed wire with a diameter of 1.29mm was produced, from the material cast in blocks, by means of hotrolling, cold drawing, and appropriate intermediate and final annealing.

For the industrially melted alloys T1-T7, a manufactured and softannealed specimen with a 1.29 mm diameter was taken from industrialproduction. A smaller quantity of the wire was drawn on the laboratoryscale up to 0.4 mm for the service life test.

For heat conductors in the form of wire, it is possible and usual to useaccelerated service life to compare materials to one another forinstance under the following conditions:

The heat conductor service life test is performed on wires having a 0.40mm diameter. The wire is clamped between 2 current supplies spaced 150mm apart and heated by applying a voltage up to 1150° C. Heating at1150° C. is performed for 2 minutes, then the current supply isinterrupted for 15 seconds. At the end of the service life, the wirefails because the cross-section melts. The burn time is sum of the “on”times during the service life of the wire. The relative burn time tb isthe % of the burn time for a reference batch.

For examining the dimensional stability, the sagging behavior of heatingcoils at the application temperature is investigated in a sagging test.For heating coils, in this test coil sagging from the horizontal isdetermined after a certain period of time. The less sagging, the greaterthe dimensional stability and creep resistance of the material.

For this test, soft annealed wire with a 1.29 mm diameter is wound intospirals having a 14 mm interior diameter. In total, 6 heating coils,each having 31 windings, are produced for each batch. All of the heatingcoils are regulated at a uniform starting temperature of 1000° C. at thebeginning of the test. A pyrometer determines the temperature. The testis performed at constant voltage in a cycle of 30 s “on”/30 s “off”. Thetest concludes after 4 hours. Once the heat coils have cooled off,sagging of the individual coils from the horizontal is measured and themean of the 6 values is found. These figures (mm) are entered into Table4b.

Table 4a and 4b list examples for the alloys in accordance with theprior art T1 through T7. T1 and T2 are alloys having approx. 30% nickel,approx. 20% Cr, and approx. 2% Si. They contain additions of rare earths(SE), in this case cerium mixed metal, which means that SE comprises 60%Ce, approx. 35% La, and the remainder Pr and Nd. The relative burn timeis 24% or 335%.

Example T3 is an alloy having approx. 40% nickel, approx. 20% Cr, andapprox. 1.3% Si. It contains additions of rare earths (SE), in this casecerium mixed metal, which means that SE is approx. 60% Ce, approx. 35%La, and the remainder Pr and Nd. The relative burn time is 72%.

Examples T4 through T7 are alloys having approx. 60% nickel, approx. 16%Cr, and approx. 1.2-1.5% Si. They contain additions of rare earths (SE),in this case cerium mixed metal, which means that SE is approx. 60% Ce,approx. 35% La, and the remainder Pr and Nd. The relative burn timeranges from 100 to 130%.

Moreover, Tables 4a and 4b contain a number of alloys melted on thelaboratory scale. The alloy according to the prior art T8 melted on thelaboratory scale is an alloy having 36.2% nickel, 20.8% Cr, and 1.87%Si.

Like the industrially produced alloys T1-T7, it contains additions ofrare earths (SE) in the form of cerium mixed metal, which means that SEis approx. 60% Ce, approx. 35% La, and the remainder Pr and Nd, and,apart from the Ni, Cr, and Si content, was melted in the same way as theindustrial batches. The batches according to the prior art T1 through T8are thus directly comparable. The relative burn time for T8 is 53%.

For the inventive tested alloys that were melted on the laboratoryscale, V771 through V777, V 1070 through V 1076, V1090 through V1093,the Ni content is approx. 36%, the Cr content is approx. 20% and the Sicontent is approx. 1.8%. The additions of Ce, La, Y, Zr, Hf, Ti, Al, Ca,Mg, C, and N were varied. These batches can therefore be compareddirectly to the alloy from the prior art T8, which thus acts as thereference alloy for optimization purposes.

Ce and La are added to V771 through V777, V1070, V1071, and V1076 byadding cerium mixed metal. In addition to Ce and La, these batchestherefore contain slight quantities of Pr and Nd, but these have notbeen explicitly added to Table 4a because the quantities are so small.

As stated in the foregoing, elements with an affinity for oxygen improveservice life. They do this in that they are included in the oxide layerand there block the diffusion paths of the oxygen on the grainboundaries. The quantity of the elements available for this mechanismmust therefore be scaled to the atomic weight in order to be able tocompare the quantities of different elements to one another.

The potential of the effective elements (PwE) is therefore defined as

PwE=200·Sum(X _(E)/atomic weight of E)

where E is the element in question and X_(E) is the content of theelement in question in percent.

FIG. 1 is a graphic depiction of the relative burn time tb and thepotential PwE for the various alloys listed in Tables 4a and 4b. Area A:Usual content of effective elements; Area B: possible content ofeffective elements; Area C: content of effective elements is too high.

When comparing T6 to T7, it is evident that the content of SE is thesame, but T7 has a lower content of Ca and Mg, despite a slightly longerservice life. It seems that Ca and Mg are no longer among the effectiveelements when in the presence of SE, that is, Ce or La. These twoelements are not included in the potential for the effective elementsbecause in the laboratory melts without SE, that is Ce or La, Ca or Mgis always less than or equal to 0.001%.

The addition for the potential of the effective elements PwE wastherefore performed using Ce, La, Y, Zr, Hf, and Ti. If there is nofigure for Ce or La, but rather only the combined figure for SE is givendue to the addition of cerium mixed metal, Ce=0.6 SE and La=0.35 SE isassumed for calculating the PwE.

PwE=1.43·X _(Ce)+1.49·X _(La)+2.25·X _(Y)+2.19·X _(Zr)+1.12·X_(Hf)+4.18·X _(Ti)

For alloys according to the prior art T1 through T8, PwE is between 0.11(T2 and T4) and 0.15 (T6 and T7). The alloy according to the prior artT8, which is also the reference alloy for the test melts, has a PwE of0.12.

The test melts V1090 and V1072, to which no cerium mixed metal wasadded, i.e. no Ce or La, but rather Y, demonstrate a shorter relativeburn time than T8, although, at 0.10, V1090 has a slightly lower PwE,but, at 0.18, V1072 has a greater PwE. The effect of Y does not seem tobe as good as that of Ce and/or La, so that replacing Se with Y leads toworse results compared to the prior art. With further additions of Zrand Ti (V1074) or Zr and Hf(V1092, V1073, V1091, V1093) in differentquantities it was possible to attain the service life for T8. However, aPwE of greater than 0.28 was necessary for this in every case (0.28 forV1092 and V1073; 0.50 for V1074; 0.33 for V1091; and 0.42 for V1093).This increases the costs due to a higher demand for expensive elementswith an affinity to oxygen and is therefore not advantageous.

Test melts V771 through V777, V1070, V1071 were all melted with ceriummixed metal, V1075 contains only La. Of these test melts, test meltsV1075 and V777 attained the highest relative burn time, approx. 70%. At0.36, the PwE of V777 is significantly greater than in V1075, at 0.20,which is on the edge of the PwE for the alloys according to the priorart. It is thus apparent that a high quantity of elements with anaffinity to oxygen is not critical for attaining a high relative burntime, but rather it is much more important to add defined elements withan affinity to oxygen. V77 attained a similarly good relative burn timewith a combination of 0.06% Ce, 0.02% La, 0.03% Zr, and 0.04% Ti.However, a much greater PwE of 0.36 is needed for this than with V1075.Although it contains the same quantity of La as V1075, the relative burntime for V772 is slightly less than for V1075 and V777. If the contentof elements with an affinity to oxygen is too high, this leads toincreased inner oxidation and thus the ultimate effect is a reduction inthe relative burn time. Thus it does not appear useful for the PwE tosignificantly exceed 0.36. At 0.23, the PwE for V771 is only slightlygreater than that for V1075, but the relative burn time is significantlyless. In V771, a majority of the elements with an affinity to oxygencomprises Ce and only the smaller portion comprises La. Consequently itseems that La is much more effective as an addition that improves burntime than Ce. Evidently this also cannot be compensated by a significantincrease in both Ce, to 0.17% and La, to 0.08%, as V773, with a nearlyequivalent relative burn time of 58%, demonstrates with an increased PwEof 0.36. This confirms the assertion, made in the foregoing, that a PwEthat is significantly greater than 0.36 does not make sense. But evenwith a PwE of 0.22, as for V776, with a relative burn time of 59%, acombination of Ce=0.06% and La=0.02% and Zr=0.05% does not seem aseffective as the addition of just La in V1075, which means that even Zris not as effective as La. The same applies for further addition of Y toCe and La, as V774 (PwE=0.28) demonstrates and a combination of Ce, La,Zr, and Hf, as V1070 (PwE=0.19) demonstrates. A 1.7-fold increase in thePwE to 0.32 for the combination Ce, La, Zr, and Hf only extends therelative burn time by 11.15-fold for V1076, which again demonstratesthat PwEs that are too high are not as effective. This is again evidentwhen comparing V1071 to V777. V1071 has the same content of Ce, La, andZr as V777, but its T1 content is significantly higher, which means aPwE of 0.44 and, in comparison to V777, a significantly lower burn timeof only 49%. At 0.07% Ce and 0.03% La, 0.005% Y, and 0.03% Hf, with aPwE of 0.30, V775 has a relative burn time of only 46%, which indicatesthat adding Y and Zr to Ce and La is not very effective.

FIG. 2 is a graphic depiction of the relative burn time and PwE to helpclarify the information in the foregoing. FIG. 2 depicts the relativeburn times for the alloys T1 through T8 according to the prior art as afunction of the nickel content. The straight lines limit the relativeburn time scatter band into which the alloys according to the prior artfall as a function of nickel content.

Also plotted is the test alloy V1075 with the addition of the mosteffective element, La. Its service life is clearly above the scatterband.

Table 4b summarizes sagging and the grain size of the wires. The alloysaccording to the prior art T1 through T8 exhibit sagging between 4.5 and6.2 mm with comparable grain sizes between 20 and 25 μm.

FIG. 3 plots nickel content. However, nickel content does not appearcritical for sagging.

FIG. 4 plots C content for alloys T1 through T8 and the test alloys.Since the test alloys have different grain sizes, they were divided into2 categories: grain sizes of 19 to 26 μm and grain sizes of 11 to 16 μm.The alloys T1 through T8 and the test alloys having a grain size of 19μm to 26 μm that have comparable grain sizes all exhibit similarsagging, ranging from 4.5 to 6.2 mm. The test alloys that have a grainsize of 11 to 16 μm and a carbon content less than 0.042% exhibitgreater sagging, approx. 8 mm, as is to be expected due to the smallergrain size. The test alloys having a grain size of 11 to 16 μm and acarbon content greater than 0.044% unexpectedly exhibit less sagging,2.8 to 5 mm.

FIG. 5 plots N content for the alloys T1 through T8 and the test melts.The alloys T1 through T8 and the test alloys having a grain size of 19μm to 26 μm that all have comparable grain sizes exhibit reduced saggingas the N content rises. As is to be expected, the test alloys that havea grain size of 11 to 16 μm and an N content less than 0.010% exhibitgreater sagging than all of the alloys having a grain size of 19 to 26μm. The test alloys having a grain size of 11 to 16 μm and a carboncontent greater than 0.044%, and that also have a nitrogen contentgreater than 0.045%, unexpectedly exhibit equal or less sagging than allof the alloys having a grain size of 19 to 26 nm.

FIG. 6 plots the total C+N. It again illustrates how C+N togethersignificantly reduce sagging. The alloys T1 through T8 and the testalloys having a grain size from 19 μm to 26 μm, which all havecomparable grain sizes, exhibit less sagging as C+N content increases.As is to be expected, due to the grain size the test alloys that have agrain size of 11 to 16 μm and a C+N content less than 0.060% exhibitgreater sagging than all of the alloys having a grain size of 19 to 26μm. The test alloys having a grain size from 11 to 16 μm and a C+Ncontent greater than 0.09%, comprising a carbon content greater than0.044% and at the same time a nitrogen content greater than 0.045%,unexpectedly exhibit sagging equal to or less than all alloys having agrain size of 19 to 26 μm.

A higher C or N content thus causes such a sharp reduction in saggingthat the effect of a smaller grain size, which increases sagging, is notcompletely compensated. The test alloys were all subjected to a standardheat treatment.

As Table 4b illustrates, smaller grain sizes occur especially with a Ccontent greater than 0.04%. When the standard heat treatment is changedto slightly higher temperatures at which the larger grain sizes thenoccur, a further reduction in sagging can be attained in these alloyshaving a C content greater than 0.04%.

The alloy V777 exhibits the least sagging of all of the alloys. It hasthe highest C content and the N content is in the top third. High Ccontent consequently seems particularly effective in reducing sagging.

Nickel contents below 34% have too negative an impact on service life(relative burn times), the specific electrical resistance, and the ctvalue. Therefore 34% is the lower limit for nickel content. Nickelcontent that is too high increases costs due to the high cost of nickel.Therefore 42% should be the upper limit for nickel content.

Cr content that is too low means that the Cr concentration drops belowthe critical limit too fast. Therefore 18% Cr is the lower limit forchromium. Cr content that is too high has a negative impact on theprocessability of the alloy. Therefore 26% Cr is the upper limit.

Formation of a silicon oxide layer beneath the chromium oxide layerreduces the oxidation rate. Below 1% the silicon oxide layer has toomany gaps to attain its full potential. Si content that is too high hasa negative effect on the processability of the alloy. Therefore an Sicontent of 2.5% is the upper limit.

A minimum content of 0.01% La is necessary to retain the effect of theLa, which increases oxidation resistance. The upper limit is 0.26%,which corresponds to a PwE of 0.38. Greater PwE values do not makesense, as explained in the examples.

Al is required for improving the processability of the alloy. Thereforea minimum content of 0.05% is necessary. If the content is too high,this has a negative effect on processability. The Al content istherefore limited to 1%.

A minimum content of 0.01% C is necessary for good dimensional stabilityand low sagging. C is limited to 0.14% because this element reducesoxidation resistance and processability.

A minimum content of 0.01% N is necessary for good dimensional stabilityand low sagging. N is limited to 0.14% because this element reducesoxidation resistance and processability.

For Mg, a minimum content of 0.001% is necessary because this improvesthe processability of the material. The limit is set at 0.05% in ordernot to soften the positive effect of this element.

The sulfur and boron content should be kept as low as possible becausethese surfactant elements have a negative effect on oxidationresistance. Therefore limits are set at max. 0.01% S and max. 0.005% B.

Copper is limited to max. 1% because this element reduces oxidationresistance.

Pb is limited to max. 0.002% because this element reduces oxygenresistance. The same applies to Sn.

A minimum content of 0.01% Mn is necessary for improving processability.Manganese is limited to 1% because this element reduces oxidationresistance.

TABLE 1 Alloys according to DIN 17470 and 17742 (Composition ofNiCr8020, NiCr7030, NiCr6015). Provided in % by weight. W no. Cr Ni +Co* Fe Al Si Mn C Cu P S NiCr8020 2.4869 19-21 >75 <1.0 <0.3 0.5-2.0<1.0 <0.15 <0.5 <0.020 <0.01

NiCr7030 2.4658 29-32 >60 <5.0 <0.3 0.5-2.0 <1.0 <0.10 <0.5 <0.020 <0.01

NiCr6015 2.4867 14-19 >59 18-25 <0.3 0.5-2.0 <2.0 <0.15 <0.5 <0.020<0.01

NiCr3020 1.4860 20-22 28.0-31.0 Remainder 2.0-3.0 <1.5 <0.2 <0.045 <0.03

NiCr2520 1.4843 22-25 19.0-22.0 Remainder 1.5-2.5 <2.0 <0.2 <0.045 <0.03

*Max. 1.5% Co

indicates data missing or illegible when filed

TABLE 2 Alloys according to ASTM B 344-83. Provided in % by weight CrNi + Co* Fe Si Mn C S ρ (μΩm) ct (at 8

80 Ni, 20 Cr 19-21 Remainder <1.0 0.75-1.75 <1.0 <0.15 <0.01 1.081 1.008

60 Ni, 16 Cr 14-18 >57 0.75-1.75 <1.0 <0.15 <0.01 1.122 1.073

35 Ni, 20 Cr 18-21 34-37 Remainder 1.0-3.0 <1.0 <0.15 <0.01 1.014 1.214

indicates data missing or illegible when filed

TABLE 3 Commercially available alloys. Provided in % by weight. 1486214862 14862 Nicrofer Nicrofer Nicrofer 3718- 3718So- 3716So- 24889 Alloy330- Inconel Bright Alloy DS- Alloy DS- Nicrofer Cronifer CroniferNicrofer 353Ma DB 330 Alloy 35 DB Band 3519Nb Cronifer II III 45 45TM Ni35 33-37 34-37 34-37 34.5-41   35-39 35.2-35.8 57-59 30-32 45-48 45-50Cr 25 15-17 17-20 18-21 17-19 17-19 19.2-19.8 14-17 19.5-21.5 22-2426-29 Si 1.3 1-2 0.75-1.5  1.0-3.0 1.9-2.6 1.9-2.5 1.9-2.5  1.0-1.751.8-3   1.5-2.2 2.5-3   Al Max. 2 Max. 0.3 Max. 0.3 Max. 0.3 Max. 0.2

Mn Max. 2 Max. 1 0.8-1.5 0.8-1.5 1.5 Max. 1.0 Max. 1.0 Max. 1 Nb 0.9 CuMax. 0.5 Max. 0.5 Max. 0.3

Ti Max. 0.2 Max. 0.2 Max. 0.2 1.5 sE Yes  0.03 Max. Max. Max. 0.05-0.150.04 0.10 0.04 Ce Yes N 0.17 0.17 C Max. Max. 0.15 Max. Max. 0.10 Max.0.10 Max. Max. 0.05-0.12 0.05 0.08 0.01 0.08 S Max. 0.015 Max. Max. Max.0.03 Max. 0.03 0.15 0.01 P Max. 0.045 Max. Max. Max. 0.03 Max. 0.03 0.010.015 B Fe Remainder Remainder Remainder Remainder Remainder RemainderRemainder Remainder Remainder Remainder

indicates data missing or illegible when filed

TABLE 4a Relative burn time tb and composition of test batches (batchno. begins with V) and batches according to the prior art (T1 throughT8). All information provided in % by weight. SE = Sum (Ce, La, Pr, Nd).If there is no information for Ce or La but there is information for SE,0.6 SE was used for Ce and 0.35 was used for La. Chg = Batch Variant ChgTb in % Ni Cr Si Al Mn Se Ce La Zr Y Hf

Cronifer III T1 24 30.7 20.3 2.05 0.05 0.34 0.10 <0.01 <

Cronifer III T2 35 31.0 21.0 2.13 0.06 0.37 0.08 <0.01 <

Ni40Cr20Si T3 72 41.6 20.7 1.36 0.31 0.46 0.06 <0.01 0

Cronifer II T4 97 59.2 16.2 1.23 0.30 0.30 0.08 <0.01 0

Cronifer II T5 106 59.5 16.1 1.5 0.22 0.25 0.05 0.01 0

Cronifer II T6 122 59.1 16.2 1.41 0.28 0.26 0.06 0.01 0

Cronifer II T7 128 59.4 16.1 1.26 0.30 0.29 0.06 0.01 0

Ni36Cr20Si T8 53 36.2 20.8 1.87 0.03 0.43 0.08 0.06 0.02 <0.01 <0.01<0.01 <

Ni36Cr20SiSE V771 56 35.2 20.6 1.79 0.05 0.45 0.12 0.04 <0.01 <0.01

Ni36Cr20SiSE V772 61 34.0 20.3 1.82 0.15 0.48 0.25 0.12 <0.01 <0.01

Ni36Cr20SiSE V773 58 35.4 20.3 1.82 0.13 0.47 0.17 0.08 <0.01 <0.01

Ni36Cr20SiSEY V774 59 35.8 19.3 1.76 0.08 0.35 0.09 0.04 0.04 <0.01

Ni36Cr20SiSEYHf V775 46 34.7 19.4 1.81 0.06 0.36 0.07 0.03 0.05 0.03 <0

Ni36Cr20SiSEZr V776 59 35.9 20.7 1.76 0.08 0.37 0.06 0.02 0.05 <0.01<0.01

Ni36Cr20SiSETiZr V777 68 37.2 20.6 1.77 0.09 0.39 0.06 0.02 0.03 <0.01<0.01 0

Ni36Cr20SiSEZrHf V1070 50 36.1 20.7 1.82 0.05 0.42 0.05 0.02 0.03 <0.010.02 <0

Ni36Cr20SiSEZrTi V1071 49 36.1 20.9 1.85 0.04 0.43 0.06 0.02 0.03 <0.01<0.01 0

Ni36Cr20SiY V1072 37 34.8 22.1 1.78 0.04 0.43 <0.01 <0.01 <0.01 <0.010.08 <0.01 <0

Ni36Cr20SiYZrHf V1073 51 35.2 20.8 1.76 0.05 0.43 <0.01 <0.01 <0.01 0.050.07 0.02 <0

Ni36Cr20SiYZrTi V1074 48 34.3 21.8 1.73 0.05 0.41 <0.01 <0.01 <0.01 0.040.07 <0.01 0

Ni36Cr20SiLa V1075 69 36.2 20.5 1.78 0.05 0.41 <0.01 0.13 0.0001 <0.01<0.01 0.

Ni36Cr20SEZrHf V1076 57 35.1 20.7 1.80 0.05 0.43 0.09 0.03 0.03 <0.010.08 <0

Ni36Cr20SiY V1090 33 35.6 20.1 1.70 0.05 0.42 <0.01 <0.01 <0.01 <0.010.05 <0.01 <0

Ni36Cr20SiYZrHf V1091 51 35.6 20.2 1.74 0.06 0.42 <0.01 <0.01 <0.01 0.060.07 0.04 <0

Ni36Cr20SiYZrHf V1092 48 35.7 20.2 1.73 0.07 0.41 <0.01 <0.01 <0.01 0.050.063 0.029 <0

Ni36Cr20SiYZrHf V1093 54 35.8 20.4 1.80 0.07 0.43 <0.01 <0.01 <0.01 0.080.08 0.06 <0

indicates data missing or illegible when filed

TABLE 4b continued: Relative burn time tb and composition of testbatches (batch no. begins with V) and batches according to the prior art(T1 through T8). Provided in % by weight. Tb Sagging KG Variant VariantChg in % in mm in μm C N P S Mo B Co Nb

Cronifer III Cronifer III T1 24 0.036 0.047 0.011 0.002 0.04 0.001 0.05<0.

Cronifer III Cronifer III T2 35 0.047 0.043 0.01 0.002 0.03 0.001 0.08<0.

Ni40Cr20Si Ni40Cr20Si T3 72 4.5 25 0.023 0.065 0.008 <0.002 <0.01 0.0010.03 0.0

Cronifer II Cronifer II T4 97 0.019 0.038 0.006 0.0013 0.03 0.004 0.04<0.

Cronifer II Cronifer II T5 106 5.2 20 0.012 0.050 0.005 0.0006 0.010.003 0.04 0.0

Cronifer II Cronifer II T6 122 5.4 22 0.016 0.046 0.005 0.0012 0.020.003 0.05 0.0

Cronifer II Cronifer II T7 128 4.8 22 0.014 0.048 0.005 0.0007 0.010.004 0.03 0.0

Ni36Cr20Si Ni36Cr20Si T8 53 6.2 22 0.034 0.031 0.002 0.0015 <0.01 0.002Ni36Cr20SiSE SE V771 56 3.7 11 0.055 0.050 0.002 0.001 <0.01 <0.001Ni36Cr20SiSE SEAl V772 61 4.0 11 0.054 0.070 0.002 0.0024 <0.01Ni36Cr20SiSE SEAl V773 58 5.0 11 0.057 0.070 0.002 0.0025 <0.01Ni36Cr20SiSEY SEY V774 59 4.1 13 0.047 0.061 0.003 0.0022 0.001Ni36Cr20SiSEYHf SEYHf V775 46 3.6 16 0.046 0.066 0.002 0.0016 0.001 0.01Ni36Cr20SiSEZr SEZr V776 59 3.9 16 0.044 0.057 0.002 0.0023 0.01 <0.001Ni36Cr20SiSETiZr SETiZr V777 68 2.8 13 0.071 0.055 0.002 0.0022 0.01Ni36Cr20SiSEZrHf SEZrHf V1070 50 5.2 22 0.030 0.030 0.002 0.0015 <0.010.001 <0.01 Ni36Cr20SiSEZrTi SEZrTi V1071 49 6.0 19 0.026 0.032 0.0020.0019 <0.01 0.001 <0.01 Ni36Cr20SiY Y V1072 37 5.7 22 0.020 0.032 0.0020.0012 <0.01 0.001 <0.01 Ni36Cr20SiYZrHf YZrHf V1073 51 5.7 19 0.0220.025 <0.002 0.0014 <0.01 0.001 <0.01 Ni36Cr20SiYZrTi YZrTi V1074 48 5.719 0.020 0.020 0.002 0.0017 <0.01 0.001 <0.01 Ni36Cr20SiLa La V1075 696.0 22 0.022 0.022 0.002 0.0024 <0.01 0.001 <0.01 Ni36Cr20SEZrHf SEZrHfV1076 57 5.1 22 0.022 0.029 0.0014 <0.01 0.001 <0.01 Ni36Cr20SiY YnNV1090 33 6.1 26 0.021 0.006 <0.002 0.0018 <0.01 0.002 <0.01 <0.01

Ni36Cr20SiYZrHf YZrHfnN V1091 51 8.5 16 0.021 0.006 <0.002 0.0018 <0.010.002 <0.01 <0.01

Ni36Cr20SiYZrHf YZrHfnCN V1092 48 7.8 16 0.007 0.008 <0.002 0.0019 <0.010.002 <0.01 <0.01

Ni36Cr20SiYZrHf YZrHfnNhC V1093 54 7.8 16 0.042 0.005 <0.002 0.0014 0.010.002 <0.01 <0.01

indicates data missing or illegible when filed

1. An iron-nickel-chromium-silicon alloy comprising, in % by weight, 34to 42% nickel, 18 to 26% chromium, 1.0 to 2.5% silicon, and furthercomprising, as additives; 0.05 to 1% Al, 0.01 to 1% Mn, 0.01 to 0.26%lanthanum, 0.0005 to 0.05% magnesium, 0.01 to 0.14% carbon, 0.01 to0.14% nitrogen, no more than 0.01% sulfur, no more than 0.005% B,remainder being iron and the usual impurities resulting from theproduction process.
 2. The alloy of claim 1, wherein the nickel contentis 34 to 39% by weight.
 3. The alloy of claim 1, wherein the nickelcontent is 34 to 38% by weight.
 4. The alloy of claim 1, wherein thenickel content is 34 to 37% by weight.
 5. The alloy of claim 1, whereinthe nickel content is 37 to 38% by weight.
 6. The alloy claim 1 whereinthe chromium content is 20 to 24% by weight.
 7. The alloy of claim 1,wherein the chromium content is 21 to 24% by weight.
 8. The alloy ofclaim 1 having wherein the a silicon content is 1.5 to 2.5% by weight.9. The alloy of claim 1, wherein the silicon content is 1.0 to 1.5% byweight.
 10. The alloy of claim 8, wherein the silicon content is 1.5 to2.0% by weight.
 11. The alloy of claim 8, wherein the silicon content is1.7 to 2.5% by weight.
 12. The alloy of any one of claim 1, wherein thesilicon content is 1.2 to 1.7% by weight.
 13. The alloy of any one ofclaim 1, wherein the silicon content is 1.7 to 2.2% by weight.
 14. Thealloy of claim 8, wherein the silicon content is 2.0 to 2.5% by weight.15. The alloy of claim 1, wherein the aluminum content is 0.1 to 0.7% byweight.
 16. The alloy of claim 1, wherein the manganese content is 0.1to 0.7% by weight.
 17. The alloy of claim 1, wherein the lanthanumcontent is 0.01 to 0.2% by weight.
 18. The alloy of claim 17, having alanthanum content of 0.02 to 0.15%.
 19. The alloy of claim 17, having alanthanum content of 0.04 to 0.15%.
 20. The alloy of claim 1, having anitrogen content of 0.02 to 0.10% nitrogen.
 21. The alloy of claim 1,having a nitrogen content of 0.03 to 0.09%.
 22. The alloy of claim 1,having a carbon content of 0.04 to 0.14%
 23. The alloy of claim 22,having a carbon content of 0.04 to 0.10%.
 24. The alloy of claim 1,having a magnesium content of 0.001 to 0.05%.
 25. The alloy of claim 24,having a magnesium content of 0.008 to 0.05%.
 26. The alloy of claim 1,having no more than 0.005% sulfur and no more than 0.003% B.
 27. Thealloy of claim 1, further comprising, by weight, 0.0005 to 0.07% Ca. 28.The alloy of claim 27 further comprising, by weight, 0.001 to 0.05% Ca.29. The alloy of claim 28 further comprising, by weight, 0.1 to 0.05%Ca.
 30. The alloy of claim 1 further comprising, by weight, as additive,0.01 to 0.3%, in total, of at least one of the elements Ce, Y, Zr, Hf,Ti.
 31. The alloy of claim 30 wherein the sumPwE=1.43·X_(Ce)+1.49·X_(La)+2.25·X_(Y)+2.19·X_(Zr)+1.12·X_(Hf)+4.18X_(Ti)is less than or equal to 0.38, PwE is the potential of the effectiveelements and X is the number corresponding to the percentage content ofthe element identified in the respective subscript.
 32. The alloy ofclaim 31 wherein content, in total, of one or more of the elementsselected from La, Ce, Y, Zr, Hf, and Ti wherein is 0.01 to 0.2% and thesumPwE=1.43·X_(Ce)+1.49·X_(La)+2.25·X_(Y)+2.19·X_(Zr)+1.12·X_(Hf)+4.18·X_(Ti)is less than or equal to 0.36, PwE is the potential of the effectiveelements and X is the number corresponding to the percentage content ofthe element identified in the respective subscript.
 33. The alloy ofclaim 32 wherein content, in total, of one or more of the elements La,Ce, Y, Zr, Hf, and Ti is 0.02 to 0.15% and the sumPwE=1.43·X_(Ce)+1.49·X_(La)+2.25·X_(Y)+2.19·X_(Zr)+1.12·X_(Hf)+4.18·X_(Ti)is less than or equal to 0.36, wherein PwE is the potential of theeffective elements and X is the number corresponding to the percentagecontent of the element identified in the respective subscript.
 34. Thealloy of claim 1 further comprising, by weight, 0.001 to 0.020%phosphorus.
 35. The alloy of claim 34, wherein the phosphorus content is0.005 to 0.020% by weight.
 36. The alloy of claim 1 further comprising,0.01 to 1.0% by weight, in total, of one or more of the elements Mo, W,V, Nb, Ta, Co.
 37. The alloy of claim 36 wherein content, by weight, intotal, of one or more of the elements Mo, W, V, Nb, Ta, Co is 0.01 to0.2%.
 38. The alloy of claim 37 further comprising, 0.01 to 0.06% byweight, in total, of one or more of the elements Mo, W, V, Nb, Ta, Co.39. The alloy of claim 38, wherein the impurities comprise not more than1.0% Cu, not more than 0.002% Pb, not more than 0.002% Zn, and not morethan 0.002% Sn.
 40. An electrical heating element comprising the alloyin accordance with claim
 1. 41. An electrical heating element thatrequires good dimensional stability and low sagging, comprising thealloy in accordance with claim
 1. 42. A furnace comprising the alloy inaccordance claim
 1. 43. An iron-nickel-chromium-silicon alloycomprising, in % by weight; 34 to 42% nickel, 18 to 26% chromium, 1.0 to2.5% silicon, and, as additives, in percent by weight, 0.05 to 1% Al,0.01 to 1% Mn, 0.01 to 0.26% lanthanum, 0.0005 to 0.05% magnesium, 0.01to 0.14% carbon, 0.01 to 0.14% nitrogen, the alloy further having 0.01to 0.3% of at least one of Ce, Y, Zr, Hf, and Ti, wherein the sumPwE=1.43·X _(Ce)+1.49·X _(La)+2.25·X _(Y)+2.19·X _(Zr)+1.12·X_(Hf)+4.18·X _(Ti) is less than or equal to 0.36, PwE is the potentialof the effective elements and X is the number corresponding to thepercentage content of the element identified in the respectivesubscript, the alloy also having common impurities from the productionprocess.